Embodiments described below relate to process field devices. In particular, the embodiments relate to capacitive sensors in process environments.
Some microelectronic circuit elements are rated to be used in ambient temperatures of no greater than 85° C. However, in many process control environments, the ambient or process temperature can exceed 200° C. As a result, standard electronics cannot be used to measure process variables such as pressure, motion, humidity, proximity and chemical concentration in these high-temperature environments. Instead, high-temperature electronics that are specifically designed to withstand temperatures in excess of 200° C. must be used. Unfortunately, such high-temperature electronics are much more expensive than standard electronics.
In addition, field devices in these high-temperature environments must be able to communicate with a control room in order to convey the process variable they are measuring. In some configurations, a very long conductor that extends between the high-temperature environment and a cooler environment is used for communication. For example, deep gas drilling occurs at depths greater than 15,000 feet. In order to monitor the state of the environment at the bottom of such wells, sensor assemblies need to be placed there. However, communication between such sensor assemblies and the top of the well is through a cable that extends the entire length of the well. Such cables have inherent line inductance, capacitance and resistance that degrade signals sent over the cables and can introduce signal ringing in the cables. The amount of inductance, capacitance and resistance in the cable is a function of the length of the cable. As the cable length increases, the inductance, capacitance and resistance increase and the degradation of the signal increases. This makes it difficult to transfer process variable values from the measurement environment to the control room.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.